Preparation And Tribological Property Of Super-Thick Diamond-like Carbon Films

Based on the direction of looking for a substitute for traditional hard chromium plating?HCP?materials.Super-thick diamond-like carbon?DLC?films were obtained by plasma enhanced chemical vapor deposition?PECVD?.The mechanical and tribological properties of films were studied,and the mechanism of the super-thick DLC films was explained with the finite element simulation.The main results are as following:?1?Different Si doped DLC films were prepared,and the effect of Si content on the properties of DLC films was studied.The results show that Si doping reduces the surface particle size and the internal stress of DLC films.The friction coefficient of DLC film can be effectively reduced by controlling the Si content in the film.The content of Si has different effects on the tribological properties of DLC films at different humidity.?2?Super-thick DLC films??Si_x-DLC/Si_y-DLC?_n?with thickness of 5.5?m?28.3?m were successfully deposited on stainless steel,aluminum alloy and copper alloy substrates.The structure,mechanical and tribological properties of the films were studied.The results show that with the increase of film thickness,the stress caused by the incompatibility of substrate and film affects the hardness and adhesion.The internal stress of the film affects the change of the bonding stress on different substrates.Stainless steel,aluminum alloy,and copper alloy have a lattice matching with carbon,and the thermal expansion coefficient gaps become larger in turn.This causes uneven distribution of the film stress.At the same time,due to the large hardness gradient,a large surface deformation occurs during the friction process,which leads to an increase in the friction coefficient of the film.Finite element simulation of the stress distribution of an super-thick?Si_x-DLC/Si_y-DLC?_n film deposited on different substrates under external force.It was found that the base material would affect the stress at the film-based interface and the heterogeneous interface.This will directly lead to the failure of the film.As a result,the super-thick DLC carbon-based films deposited on different substrates show different wear conditions.?3?The optimized structure and tribological properties of super-thick?Si_x-DLC/Si_y-DLC?_n/DLC films were studied.The results show that the structure of?Si_x-DLC/Si_y-DLC?_n/DLC films changes when the modulation period is greater than 1.70?m.With the decrease of modulation period,the thinner monolayer weakens the motion of atoms and accelerates the"thermal peak"effect in the deposition process.Thus,the internal stress of the film is reduced.The tribological properties of super-thick DLC films with different modulation periods in air and water were explored.The study found that the run-in period of super-thick DLC films was gradually shortened as the modulation period increased in the air.The friction coefficients of the films was reduced to about 0.05.After the failure of the top pure DLC layer in the water environment,the friction coefficient of the super-thick DLC film increased to about0.13.The wear rate of the film increases as the modulation period increases.The modulation ratio has a significant effect on the mechanical properties of?Si_x-DLC/Si_y-DLC?_n/DLC films.As the proportion of Si_x-DLC layers increases,the internal stress of the films decreases,the bonding stress increases,and the hardness decreases.At low load,the friction coefficient can reach as low as 0.03,and the wear rate is positively related to the hardness of the top pure DLC layer.The peeling of the transfer film under high load and the SiO₂ wear debris cause fluctuation and increase of the friction coefficient.The wear rate was positively correlated with the hardness of the super-thick DLC film.